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Kinematics and Abundances of the Bulge The Bulge Radial Velocity/Abundance Assay

Explore the dynamics, formation, and composition of the Milky Way bulge at the 3rd Subaru Science Conference. Learn about pseudobulges, bar models, and age/chemistry constraints from studies by leading astrophysicists.

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Kinematics and Abundances of the Bulge The Bulge Radial Velocity/Abundance Assay

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  1. Kinematics and Abundances of the BulgeThe Bulge Radial Velocity/Abundance Assay R. Michael Rich (UCLA), Christian Howard, (SOFIA), Andreas Koch (Leicester), Juntai Shen (Shanghai Observatory), HongSheng Zhao (St. Andrews), John Kormendy (UT Austin), Will Clarskon (UCLA) Roberto de Propris (CTIO), Christian Johnson (UCLA), Jon Fulbright(JHU), Livia Origlia (Bologna) Annie Robin (Besancon), Mario Soto (La Serena), Peter Frinchaboy (TCU) 3rd Subaru Science Conference Funding: NSF AST-0709479

  2. Bulges appear be either spheroidal (classical) or barlike (pseudobulge) Canonical formation picture is that spheroidal forms via early mergers, while pseudobulges/bars evolve from a buckling instability over longer timescales. Milky Way has dynamics characteristic of pseudobulges, yet age/chemistry consistent with rapid formation. 3rd Subaru Science Conference

  3. Imelli et al. 2004; Elmegreen et al. (2008) - major merger origin Clumps dissipate rapidly into bulge or Classical early merger.. Multiple star forming clumps might produce kinematic subgroups with distinct chemical or dynamical fingerprints. Abadi 2003 Imelli et al. 2004 3rd Subaru Science Conference

  4. N-body bar models attractive for representing the bulge However, extended formation models favored; bar survival? Bar dissolves due to central mass (Norman et al. 1996) Combes 09- bar resurrection via gas inflow Vertical thickening of the bar into a bulge would leave no abundance gradient in the z-direction. 3rd Subaru Science Conference

  5. Bulge in Context 2MASS Oph SFR (foreground) Baade's Window Sgr dSph (28 kpc) Wyse et al. (1997) 3rd Subaru Science Conference Courtesy J. Fulbright

  6. Age constraint from PM separation Clarkson et al. 08 ~99% of bulge older than 5Gyr; pure 10+ Gyr likely (Clarkson+ 08, 09 3rd Subaru Science Conference

  7. Kinematics PNe Beaulieau et al. 2000 Vrot sigma Trailblazing survey used to explore a range of bar models, constrain orientation of bar 3rd Subaru Science Conference

  8. BRAVA First proposal 2003 Rich et al. 2007 ApJ 658, L29 Rich+ 2007 astro-ph/0710.5162 Howard et al. 2008 ApJ; C. Howard Ph.D. 11/08 Strategy: Use M giants brighter than clump that can be observed even in high extinction fields. M giants also trace the 2um light of the bulge Select M giants from 2MASS survey (excellent, uniform, astrometry and photometry; ease of developing links to spectra for a public database Clear red giant branch easily seen in 2MASS data; bulge membership Cross correlation from 7000 - 9000A (include Ca IR triplet) Abundances from either future IR studies or from modeling of optical spectra 3x10 min exposures with Hydra fiber spectrograph at CTIO Blanco 4m; ~100 stars/field R~4000 9,000 stars to date; website and public data release aim for 2010 3rd Subaru Science Conference

  9. Survey Fields 2005: blue 2006: red 2007: green Goal: Grid of fields at 1 deg intervals, covering 10x10 deg box, pushing as close to plane as possible 3rd Subaru Science Conference

  10. Target Selection Howard et al. 2008 b=-4 dereddened Kunder et al. 2011, new sample 3rd Subaru Science Conference

  11. Larger samples have not confirmed 2 stream candidates; all candidates will be followed up. Reitzel et al. (2007) simulations suggest ~1 “real” stream Stream followup important. Possible origins from disrupted globular clusters or dwarf galaxies, groups of stars in unusual orbit families; all candidates presently assumed to be Poisson statistics caused. 3rd Subaru Science Conference

  12. -4 -8 Zhao 3rd Subaru Science Conference

  13. 3rd Subaru Science Conference

  14. Most recent results (Kunder et al. 2011) 3rd Subaru Science Conference

  15. Major Axis showing cylindrical rotation (Fit is Shen et al. 2010) 3rd Subaru Science Conference

  16. Minor axis with Shen et al. (2010) fit 3rd Subaru Science Conference

  17. Modeling the Milky Way BulgeShen, Rich et al. 2010 • A simple model of the Galactic bulge matches the BRAVA data extremely well in almost all aspects: • b = -4o major axis • b = -8o degree major axis • l = 0o degree minor axis • Surface density • Shen, J., RMR, Kormendy et al 2010, ApJL submitted, arXiv:1005.0385 3rd Subaru Science Conference

  18. Modeling the Milky Way Bulge --- Surface Brightness Map Sun DIRBE Composite map • The bar angle from kinematic constraint is about ~ 20o • The bar’s axial ratio is about 0.5 to 0.6, and its half-length is ~4kpc 3rd Subaru Science Conference

  19. Modeling the Milky Way Bulge ---Match stellar kinematics in all strips strikingly well Black line = model; it is not a fit of data points 3rd Subaru Science Conference

  20. A Significant Classical Bulge is Excluded The data excludes a pre-existing classical bulge with mass >~ 10% Mdisk 3rd Subaru Science Conference

  21. Modeling on the MW bulge –Model Setup • High resolution N-body simulations with millions of particles • Cold massive disk, initial Q ~ 1.2 • A pseudo-isothermal rigid halo with a core which gives a nearly flat rotation curve of ~220 km/s from 5 to 20 kpc 3rd Subaru Science Conference

  22. Summary from modeling of the BRAVA kinematics • Our simple, but realistic, model can match BRAVA kinematics of the Galactic bulge strikingly well • No need for a contrived model with many free parameters • The bulge is simply the bar viewed edge-on; it is part of the disk, not a separate component. • A significant classical bulge is excluded, so our MW is an nearly pure-disk galaxy • Giant, pure-disk galaxies like our own MW present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers • Fraction of pure disk galaxies in local U. (Kormendy & Barentine 2010; Kormendy et al. 2010) • Shen, J., RMR, Kormendy et al 2010, ApJL submitted, arXiv:1005.0385 3rd Subaru Science Conference

  23. A Problem: Abundance gradient in the outer bulge Cylindrical rotation a characteristic of pseudobulges, but should not exhibit abundance gradient, since buckling models are not dissipative. Location on Binney plot similar to NGC 4565. Zoccali et al. 2008 with Johnson et al. 2011 for -8 deg 3rd Subaru Science Conference

  24. But no abundance gradient <4o (Rich, Origlia, Valenti; 2011) 3rd Subaru Science Conference

  25. The Milky Way shares much in common with NGC 4565 (peanut bulge, abudance gradient) Kormendy & Kennicutt 2004 MW 3rd Subaru Science Conference

  26. Kormendy Illingworth 82 NGC 4565 has a boxy pseudobulge, cylindrical rotation like in the Milky Way bulge, and has a steep abundance gradient in the z direction. Proctor et al. 00 3rd Subaru Science Conference

  27. The Age/Pseudobulge Paradox Clarkson et al. 08 ~99% of bulge older than 5Gyr; pure 10+ Gyr likely (Clarkson+ 08, 09 Cylindrical rotation, morphology, consistent with pseudobulge (young?) Abundance gradient of MW, NGC 4565 – but how? If N-body models? 3rd Subaru Science Conference

  28. BRAVA Main Conclusions • BRAVA is a radial velocity survey of Galactic bulge M giants • Fully public dataset with spectra at http://irsa.ipac.caltech.edu/ as well as at UCLA: http://brava.astro.ucla.edu/. • Survey to date has covered strips at b=-4, -6, -8, and the Southern minor axis • Bulge rotation curve and radial velocity dispersion profile measured • Departure from “solid body” rotation at b=-4 • Cylindrical rotation at -8 • No detection of cold streams • Coadded datasets at b=-4, -8 are Gaussian with no evidence of dynamically independent sub populations • Remarkable agreement with Shen et al. 2010 bar; “bulge”<10% Mdisk 3rd Subaru Science Conference

  29. Hydra echelle survey ongoing Johnson, Rich et al. 2011 3rd Subaru Science Conference

  30. -8o Field (Plaut’s Field) C. Johnson, Rich, Fulbright, Valenti, McWilliam (2011) CTIO Hydra, 300 stars, 4 wavelength settings 3rd Subaru Science Conference

  31. Johnson et al. 2010: alphas enhanced at -8o = 1kpc 3rd Subaru Science Conference

  32. Johnson, Rich et al. 2011: -8o Field Eu/Fe follows alpha-like trend; La/Eu r-process = rapid formation McWilliam & Rich 94, 2010 Johnson, Rich et al. 2010 3rd Subaru Science Conference

  33. In terms of heavy elements, bulge is different from thick disk Johnson, Rich et al. 2011 Foreground clump Bulge La/Eu more r-process like than thick disk 3rd Subaru Science Conference

  34. [Na/Fe] in bulge distinct from thick disk 3rd Subaru Science Conference

  35. Remarkable Cluster Ter 5 Ferraro et al. 2009 Double HB; brighter Has [Fe/H]~+0.3 Fainter has [Fe/H]~-0.2 0.5 dex [Fe/H] spread- Unique case. 3rd Subaru Science Conference

  36. Origlia, Rich et al. 2011 Keck + Nirspec (Mclean et al. 1998) 1.6 um window R=25,000 Two populations with striking composition difference Metal rich part exceeds metallicity of any Galactic globular cluster 3rd Subaru Science Conference

  37. 3rd Subaru Science Conference

  38. Subaru/Japan Collaboration Opportunities FMOS: Survey abundances and kinematics across bulge, near plane in regions of high extinction. HDS: Obtain high S/N spectroscopy at R=50,000 for extrem r- s- process enhanced bulge giants. Jasmine Missions: cross correlate radial velocities of BRAVA with proper motions from nano-Jasmine, Jasmine. Define X-shaped bulge in 3D 3rd Subaru Science Conference

  39. Jasmine will map bulge In 3 dimensions- is there an X? How much mass there? 3rd Subaru Science Conference

  40. BRAVA Implications The M giant population shows kinematic uniformity on large scales The agreement with two independent N-body bar models is striking. The dynamical processes responsible for creating a bar should accelerate stars without respect to abundance; the existence of an abundance gradient cannot be explained by N-body bar models. There is no transition in population from “bar” to “bulge/spheroid” at b=-8, that might help explain the gradient. Growing evidence (alpha/Fe, La/Eu, photometric) for early, rapid, bulge formation. However, composition alone does not rule out a younger sub population at [Fe/H]>0 3rd Subaru Science Conference

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